When you call someone using Duo, the other person can see live video of you while their device rings if they have you as a contact. You won't be able to see the person you're calling until they answer.
Important: Knock Knock is available for Google Duo 1:1 and group video calling. Knock Knock isn't available when you join a meeting in the Duo app. Learn more about changes to Google Duo.
Turn on Knock Knock
- On your Android phone or tablet, open the Duo app .
- In the top right corner, tap More options Settings Knock Knock.
- Turn on Knock Knock.
Can't see video preview for incoming call
If you can't see a video preview when someone calls you, the other caller has Knock Knock turned off or they're not in your contacts.